1. Field of the Invention
The present invention relates to an information recording medium for storing digital data, and a data processing apparatus and data processing method for moving and processing the data stored in the information recording medium.
2. Related Art
As recording media capable of reading and writing digital data, recently, various semiconductor memories are developed and used, such as SD Memory Card (registered trademark), Memory Stick (registered trademark), and CompactFlash (registered trademark).
Data processing apparatuss for processing data by using these semiconductor memories are widely used in electronic products such as personal computers, audio appliances, video appliances, mobile telephones and digital cameras.
Data stored in semiconductor memory is often managed in file format to specify address and size by using a file system. For example, the SD memory card (registered trademark) is managed by FAT (file allocation table) file system.
In such a case, by repeating writing of files and erasing of files of different sizes many times in the semiconductor memory, the management information of the FAT file system is fragmented. That is, files storing data and vacant regions are present in discrete state in the logical address space. Since the management information is complicated by fragmentation, various problems are caused, such as increase of overhead of file reading, and increase of search time of vacant region for file writing. Some of the semiconductor memories are advanced in speed of write process by writing data in a specific size, but if fragmented, vacant capacity of specific size cannot be assured, and the write process may slow down.
For example, complication of management information by fragmentation causes to lower the processing speed in the following sequence. A data processing apparatus for writing and reading data in a semiconductor memory reads out the information (for example, link information) about the file system of the semiconductor memory to use it on the RAM. Usually, due to limitation of RAM capacity, the data processing apparatus does not load all information of the file system on the RAM, but loads only part of the information of the file system to use it on the RAM. If the information necessary for data access is not present on the RAM, the portion including the necessary information is loaded again. Hence, if the degree of fragmentation is high in the logical address space, when tracing the link information loaded on the RAM, partial information of the file system must be loaded again and again on the RAM, and the processing speed is lowered.
As a method of eliminating such fragmentation, a defragmentation process is proposed for relocating the data so that the data may be disposed in consecutive recording regions (see, for example, patent document 1). In defragmentation process, data of files and vacant regions discrete in the address space are rearranged to be disposed in consecutive regions, and generally it takes a long time in the moving process of data in a physical address space. Besides, the semiconductor memory is generally limited in the number of times of reading and writing, and thus the data relocating process by defragmentation causes to shorten the service life of the semiconductor memory.
Accordingly, a method of starting defragmentation process at an adequate timing (see, for example, patent document 2), and a method of defragmenting the semiconductor memory less frequently (see, for example, patent document 3) have been proposed.
Patent document 1: JP, 2000-305818, A
Patent document 2: JP, 08-339318, A
Patent document 3: JP, 2000-322307, A
In the methods of patent documents 2 and 3, when executing the defragmentation process, the data is actually moved to relocate in the physical address space of recording regions of the semiconductor memory. Thus it still takes a substantial time in defragmentation process, and the life of the semiconductor memory may be shortened.